Nylons are polyamides which are sometimes synthesized by the condensation polymerisation of a diamine with a dicarboxylic acid. Similarly, nylons may be produced by the condensation polymerisation of lactams. A ubiquitous nylon is Nylon 6,6, which is produced by reaction of hexamethylenediamine (HMD) and adipic acid. Nylon 6 is produced by a ring opening polymerisation of caprolactam (Anton & Baird, Polyamides Fibers, Encyclopedia of Polymer Science and Technology, 2001).
Nylon 7 and Nylon 7,7 represent novel polyamides with value-added characteristics compared to Nylon 6 and Nylon 6,6. Nylon 7 is produced by polymerisation of 7-aminoheptanoic acid, whereas Nylon 7,7 is produced by condensation polymerisation of pimelic acid and heptamethylenediamine. No economically viable petrochemical routes exist to producing the monomers for Nylon 7 and Nylon 7,7.
Given no economically viable petrochemical monomer feedstocks, biotechnology offers an alternative approach via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds.
Both bioderived feedstocks and petrochemical feedstocks are viable starting materials for the biocatalysis processes.
Accordingly, against this background, it is clear that there is a need for methods for producing pimelic acid, 7-aminoheptanoate, 7-hydroxyheptanoate, heptamethylenediamine and 1,7-heptanediol (hereafter “C7 building blocks”) wherein the methods are biocatalyst-based.
However, no wild-type prokaryote or eukaryote naturally overproduces or excretes C7 building blocks to the extracellular environment. Nevertheless, the metabolism of pimelic acid has been reported.
The dicarboxylic acid, pimelic acid, is converted efficiently as a carbon source by a number of bacteria and yeasts via β-oxidation into central metabolites. β-oxidation of CoEnzyme A (CoA) activated pimelate to CoA-activated 3-oxopimelate facilitates further catabolism via, for example, pathways associated with aromatic substrate degradation. The catabolism of 3-oxopimeloyl-CoA to acetyl-CoA and glutaryl-CoA by several bacteria has been characterised comprehensively (Harwood and Parales, Annual Review of Microbiology, 1996, 50, 553-590).
The optimality principle states that microorganisms regulate their biochemical networks to support maximum biomass growth. Beyond the need to express heterologous pathways in a host organism, directing carbon flux towards C7 building blocks that serve as carbon sources rather than to biomass growth constituents, contradicts the optimality principle. For example, transferring the 1-butanol pathway from Clostridium species into other production strains has often fallen short by an order of magnitude compared to the production performance of native producers (Shen et al., Appl. Environ. Microbiol., 2011, 77(9), 2905-2915).
The efficient synthesis of the seven carbon aliphatic backbone precursor is a key consideration in synthesizing C7 building blocks prior to forming terminal functional groups, such as carboxyl, amine or hydroxyl groups, on the C7 aliphatic backbone.